My Outlook Inbox is compromised and it won't load anything except messages from a specific customer

C Groller 20 Reputation points
2026-05-20T13:03:09.21+00:00

This morning, I opened my laptop and went to Outlook in my browser (Firefox) as I do every day. Today, my inbox is only showing emails from a specific customer, and even the black borders that indicate "Today, yesterday, last week, etc." are instead marked with this customer's name, followed by a long string of characters. See below:

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Outlook | Web | Outlook on the web for business | Email
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AI answer

2026-05-20T13:03:44.6033333+00:00

This behavior is most likely caused by a filter or rule that’s limiting what appears in the Inbox, not by the mailbox being compromised.

Use these steps to restore the normal Inbox view.

  1. Clear any filters in Outlook on the web
    1. At the top of the message list, select Filter.
    2. Change the selection to All so every message is shown, not just those that match a specific condition (such as a particular sender).
  2. Check for rules that move or show only this customer’s mail
    1. Open Rules settings in Outlook on the web.
    2. Look for any Inbox or Sweep rule that references this customer’s address or domain, or that moves “all new mail” to another folder.
    3. Edit or delete any such rule that is incorrectly moving or restricting messages.
    4. Save changes and go back to the Inbox to confirm that all messages now appear.
  3. Verify other folders
    1. Check Junk Email, Archive, and other folders to see whether non‑customer messages were moved there.
    2. If messages are found, move them back to Inbox using Move to > Inbox.
  4. Rule out browser/add‑on issues
    1. Try Outlook on the web in another browser (for example, Microsoft Edge) or a private/incognito window.
    2. In Firefox, temporarily disable add‑ons (especially ad‑blockers or other extensions that modify pages), then reload Outlook. Certain Firefox add‑ons are known to prevent the Inbox from loading correctly.
  5. If the Inbox is still empty or only partially loading
    1. Follow the workaround for “Inbox empty or not loading”: disable or remove problematic Firefox add‑ons as documented, or use another browser.

If there is any concern that someone else accessed the account, review the recent sign‑in activity and secure the account as described in the referenced article.

References:

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  1. Ana Le 2,615 Reputation points Independent Advisor
    2026-05-20T13:49:42.9133333+00:00

    Hi @C Groller,

    Based on the screenshot, this does not look like a typical “hacked inbox” scenario. It looks more like Outlook on the web is failing to render/ group the mailbox correctly, possibly due to corrupted browser cache/session data, a mailbox view issue, or an extension/ script interfering with Outlook Web App.

    The long string appearing as a category/header name instead of “Today/ Yesterday/ Last week” suggests the UI is reading invalid metadata or failing to load the mailbox view properly.

    Please try these steps in order:

    1/ Open Outlook in a private/incognito window

    • Sign in to Outlook there and check whether the inbox appears normally.

    2/ Test another browser

    • Try Microsoft Edge or Chrome temporarily.
    • If the mailbox loads correctly there, the issue is likely related to Firefox cache/cookies/extensions.

    3/ Clear Outlook site data/ cache

    • In Firefox: Settings > Privacy & Security > Cookies and Site Data > Manage Data
    • Search for:
    • outlook.office.com
    • office.com
    • microsoft.com
    • Remove those entries, restart Firefox, and sign in again.

    4/ Disable browser extensions temporarily

    Especially:

    • Ad blockers
    • Privacy/security extensions
    • Script blockers
    • Mail helper add-ons

    These can sometimes break Outlook Web rendering.

    5/ Reset the Outlook view

    • Click the gear icon (Settings) in the top-right corner.
    • Select:
      • Mail > Layout
      • Under “Focused Inbox”: Select “Don’t sort my messages”
      • Under “Message organization” or “Conversation view”: Select “Do not group messages” or “Show email as individual messages”
    • Refresh the page using Ctrl + F5.

    User's image

    These changes can help determine whether the issue is related to corrupted conversation grouping or Outlook web rendering.

    6/ Check whether the issue exists in:

    • Focused Inbox
    • Other folders
    • Another user profile/browser profile
    • Outlook desktop app (if installed)

    If the same behavior appears across multiple browsers and devices, the issue may be tied to mailbox data or a service-side rendering problem, in which case the organization’s Microsoft 365 administrator should check:

    • Service Health
    • Mailbox integrity
    • Any transport/add-in integrations affecting the mailbox

    This behavior does not typically indicate that the mailbox has been compromised. It appears more consistent with a browser rendering or cached session issue affecting Outlook on the web, especially since the folder grouping labels are displaying incorrectly.

    Microsoft and other users have reported similar Outlook on the web rendering issues related to browser cache, cookies, extensions, or Firefox-specific behavior:

    Please try using an InPrivate/ Incognito window, clearing browser cache/ cookies for Outlook/ Office sites, temporarily disabling extensions, and testing another browser such as Edge or Chrome then let me know the result.

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